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[romprefix] Sanity-check the runtime segment address for PCI 3

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Some PCI 3 BIOSes seem to provide a garbage value in %bx, which should
contain the runtime segment address.  Perform a basic sanity check: we
reject the segment if it is below the start of option ROM space.  If
the sanity check fails, we assume that the BIOS was not expecting us
to be a PCI 3 ROM, and we just leave our image in situ.
This commit is contained in:
Michael Brown 2008-10-17 18:12:24 +01:00
parent 7982e79d3c
commit 5600955bdd
1 changed files with 9 additions and 0 deletions
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9
src/arch/i386/prefix/romprefix.S
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@ -205,7 +205,16 @@ init:
movb %bl, %al
call print_hex_byte
cmpb $3, %bh
jb 1f
/* PCI >=3.0: leave %gs as-is if sane */
movw %gs, %ax
cmpw $0xc000, %ax
jae 2f
/* PCI 3.0 with insane %gs value: print error and ignore %gs */
movb $'!', %al
call print_character
movw %gs, %ax
call print_hex_word
1: /* PCI <3.0: set %gs (runtime segment) = %cs (init-time segment) */
pushw %cs
popw %gs